1. Field of the Invention
The present invention relates to a reducer of an electric power steering apparatus. More particularly, the present invention relates to a reducer of an electric power steering apparatus, which can reduce a rattle noise occurring by an increase in backlash caused by abrasion of a worm and a worm wheel, or by an impact transferred from a road via a wheel and a steering shaft, thereby providing a pleasant driving condition to a driver.
2. Description of the Prior Art
FIG. 1 shows a configuration view illustrating a conventional electric power steering apparatus. As shown in FIG. 1, an electric power steering apparatus 100 includes a steering system 130 extending from a steering wheel 102 to both side wheels 126, and an auxiliary power mechanism 140 for supplying auxiliary steering power to the steering system 130.
The steering system 130 includes a steering shaft 106 whose one side is connected to the steering wheel 102 and rotates together with the steering wheel 102, and the other side is connected to a pinion shaft 108 via a couple of universal joints 104. Also, the pinion shaft 108 is connected to a rack bar 112 through a rack-pinion mechanism 110, and both ends of the rack bar 112 are connected to the wheels 126 of a vehicle through a tie rod 122 and a knuckle arm 124.
The auxiliary power mechanism 140 includes a torque sensor 142, an electronic control device 144, a motor 146, and a reducer 150. The torque sensor 142 senses a torque applied to the steering wheel 102 by a driver, and outputs an electrical signal in proportion to the sensed torque. The electronic control device 144 generates a control signal based on the electrical signal transferred from the torque sensor 142. The motor 146 generates auxiliary power based on the control signal transferred from the electronic control device 144. The reducer 150 is provided with a worm 152 and a worm wheel 156 so as to transfer the auxiliary power generated by the motor 146 to the steering shaft 106.
Accordingly, the electric power steering apparatus is configured in such a manner that the torque generated by the rotation of the steering wheel 102 is transferred to the rack bar 112 via the rack-pinion mechanism 110, and the auxiliary power generated by the motor 146 according to the generated torque is transferred to the rack bar 112.
In other words, the torque generated by the rotation of the steering wheel 102, together with the auxiliary power generated by the motor 146, allows the rack bar 112 to move in the axial direction.
FIG. 2 shows a cross-sectional view illustrating a reducer of the conventional electric power steering apparatus. As shown in FIG. 2, in the reducer 150, a worm shaft 254 formed with the worm 152 is provided, and both ends of the worm shaft 254 are provided with worm shaft bearings 257, respectively, to support the worm shaft 254. The worm shaft bearing 257 has a ball 258 combined with an inner wheel 280 and an outer wheel 270 thereof. Also, in order to prevent the worm shaft bearing 257 from playing in the axial direction of the worm shaft 254, a plug bolt 210 is fastened between a damping coupler 240 and the worm shaft bearing 257, and the plug bolt 210 is fixed by a plug nut 220.
The worm shaft 254 is configured to be connected to the motor 146 via the damping coupler 240 and to be rotated by the driving of the motor 146.
Then, at one side of the external diameter of the worm 152, the worm wheel 156 is provided in such a manner that it can be engaged with the worm 152 formed on the worm shaft 254. The worm wheel 156 is configured to be mounted to the steering shaft 106, in which to the steering shaft 106, the rotation force of the steering wheel 102 (see FIG. 1) operated by the driver is transferred, while the worm shaft 254's rotation force caused by the driving of the motor 146 is transferred to the steering shaft 106.
A gear housing 260 houses the worm 152, the worm wheel 156, and the like, and is provided with, at its one side, the motor 146 for providing the driving force to the worm shaft 254. The gear housing 260 and the motor 146 are combined with each other through a bolt 250 by a motor cover 230.
The reducer of the electric power steering apparatus, as configured above, controls the driving of a motor by an electronic control device provided in a vehicle according to driving conditions of the vehicle, and transfers a worm shaft's rotation force caused by the driving of the motor, together with a driver-driven steering wheel's rotation force, to a steering shaft. This makes it possible to keep the driver's steering driving state soft and stable.
However, the reducer of the conventional electric power steering apparatus, has a problem in that the progress in the wearing of the worm and the worm wheel rotated by the driving of the motor increases the gap between them, which causes a rattle noise due to the backlash.
Also, there is a problem in that a rattle noise occurs by an impact transferred from a road via a wheel and the steering shaft, thereby causing an unpleasant feeling for the driver during operation of the steering wheel.